1. Field of the Invention
The present invention relates to variable focus lens systems having both automatic and manual focusing means in general, and to such lens systems for photographic cameras, in particular.
2. Description of the Prior Art
Variable focus lenses and apparatus utilizing such lenses, such as photographic cameras, telescopes and the like are well known and their operation are well understood in the prior art. A camera having a variable focus lens and having a focus control system coupled to said lens for automatically focusing image-containing light rays of a remote object at the film plane of said camera in response to a rangefinder derived signal representative of the actual distance between said camera and said remote object, are known in the prior art. A camera having such a focus control system that utilizes acoustical energy to determine the distance to an object remote from said camera is described in U.S. Pat. No. 3,522,764 to BIBER et al. One arrangement that combines automatic focusing as in said BIBER et al patent with a conventional optical type couple rangefinder in a single photographic camera is described in U.S. Patent application Ser. No. 838,581 by OSTROWSKI et al.
A bidirectional focus control system, i.e., a focus control system that, once commanded to do so, can move the movable element of a variable focus lens in either of two directions from any initial position within the normal focusing range of said lens, for focusing purposes, is also known in the prior art. One example of such a system is described in the above-mentioned BIBER et al. patent.
Another type of focus control system for a variable focus lens is sometimes referred to as a unidirectional focus control system in that the movable or focusing element of such a lens is always moved from the same or known reference point for focusing purposes. While such an element is movable in either of two axial directions, no lens focusing is performed as said element moves within its focusing range toward said reference point. A unidirectional focus control system of this type is significantly less complex than a bidirectional focus control system because it is unnecessary to continuously monitor lens element movement as said element is moved toward said known reference point. The cost savings attendant a unidirectional focus control system over a bidirectional focus control system makes it attractive to the control system designer. An example of a unidirectional focus control system for a variable focus camera lens is described in U.S. Pat. No. 3,713,371 to KURIHARA et al.
In U.S. patent application Ser. No. (Case no. 5846) by SHENK, a variable focus lens is positionable to the proper subject-in-focus position by a focus control system having both manual and automatic focusing capabilities. The automatic focus control portion of said focus control system is of the unidirectional type and the proper operation of said unidirectional focus control system is dependent upon said lens being moved at least a minimum distance outside of its normal focusing range, and the actuation of a switch by such lens movement. A problem with this type of unidirectional focus control system is that it is possible to manually move the movable lens element far enough outside of its normal focusing range to actuate said switch without moving said lens said required minimum distance, which would cause the lens to be misfocused by the automatic focus control system if the automatic focus control mode is selected after the lens has been so positioned.
An important feature of the automatic focus control portion of the unidirectional focus control system disclosed in said SHENK application is its ability to always move said lens said minimum distance outside of its normal focusing range if said lens is within its normal focusing range when the automatic focus control mode is selected. If the automatic focus control system were the only means utilized to move said variable focus lens said minimum distance outside of its normal focusing range, the above-described misfocusing by said unidirectional focus control system would be avoided.